This invention relates to a catalyst component and a catalyst system which is useful for the stereoregular polymerization or copolymerization of alpha-olefins and more particularly concerns a magnesium-containing supported titanium-containing catalyst component which has superior morphology and which is formed as a precipitate from an emulsion.
Use of solid, transition metal-based, olefin polymerization catalyst components is well known in the art including such solid components supported on a metal oxide, halide or other salt such as widely-described magnesium-containing, titanium halide-based catalyst components. Such catalyst components commonly are referred to as "supported." Although many polymerization and copolymerization processes and catalyst systems have been described for polymerizing or copolymerizing alpha-olefins, an important practical consideration of preparing a catalyst component is the complexity of the preparation steps including minimization of waste streams which are created in the catalyst component manufacturing process. Consideration must be made to minimize waste solvent volume and use of certain solvents or diluents which require special environmental handling such as aromatic hydrocarbons.
Numerous individual processes or process steps have been disclosed to produce improved supported, magnesium-containing, titanium-containing, electron donor-containing olefin polymerization or copolymerization catalysts. For example, Arzoumanidis et al., U.S. Pat. No. 4,866,022, incorporated by reference herein, discloses a method for forming an advantageous alpha-olefin polymerization or copolymerization catalyst or catalyst component which involves a specific sequence of specific individual process steps such that the resulting catalyst or catalyst component has exceptionally high activity and stereospecificity combined with very good morphology. A solid hydrocarbon-insoluble, alpha-olefin polymerization or copolymerization catalyst or catalyst component with superior activity, stereospecificity and morphology characteristics is disclosed as comprising the product formed by 1) forming a solution of a magnesium-containing species from a magnesium hydrocarbyl carbonate or magnesium carboxylate; 2) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane; 3) reprecipitating such solid particles from a mixture containing a cyclic ether; and 4) treating the reprecipitated particles with a transition metal compound and an electron donor.
Arzoumanidis et al., U.S. Pat. No. 4,540,679, incorporated by reference herein, discloses a process for the preparation of a magnesium hydrocarbyl carbonate by reacting a suspension of a magnesium alcoholate in an alcohol with carbon dioxide and reacting the magnesium hydrocarbyl carbonate with a transition metal component.
Arzoumanidis et al., U.S. Pat. No. 4,612,299, incorporated by reference herein, discloses a process for the preparation of a magnesium carboxylate by reacting a solution of a hydrocarbyl magnesium compound with carbon dioxide to precipitate a magnesium carboxylate and reacting the magnesium carboxylate with a transition metal component.
Emulsions of magnesium chlorides solubilized in alcohols have been used to prepare olefin polymerization catalyst components in U.S. Pat. No. 4,399,054 and European Published Application EP 0 433 105.
In addition to catalyst yield and stereospecificity, polymer or copolymer morphology often is critical and typically depends upon catalyst morphology. Good polymer morphology generally involves uniformity of particle size and shape, resistance to attrition and an acceptably high bulk density. Minimization of very small particles (fines) typically is very important especially in gas-phase polymerizations or copolymerizations in order to avoid transfer or recycle line pluggage. Therefore, it is highly desirable to develop alpha-olefin polymerization and copolymerization catalysts and catalyst components that have good morphology, and in particular, an acceptable particle size. Another property which is important commercially is the maintenance of an acceptably high bulk density.
The purpose of this invention is to create a supported propylene polymerization catalyst system incorporating internal electron donors which shows superior polymerization activity while maintaining acceptable stereoregularity and other properties such as polymer bulk density and particle size distribution. A purpose of this invention is to produce a particulate solid catalyst component with a round morphology and typically larger particle sizes than otherwise comparably prepared material. Another purpose is to create a solid, particulate catalyst component which will produce polymer particles with improved flowability, especially for medium and high impact propylene copolymers. Another purpose of this invention is to manufacture solid catalyst components without creating large quantities of undesirable waste streams.
The solid, olefin polymerization catalyst components of this invention are substantially uniform particles with good morphology and are active in polymerization of olefins especially stereoregular polymers of propylene. In addition to these advantageous properties, the catalyst particles can be manufactured in a relatively simple process which minimizes production of undesirable waste streams.